Valves used in industrial environments often have rigorous performance standards. In the past, packings of polytetrafluoroethylene and other fluoropolymers have been used which were considered to seal valves satisfactorily. While packings were previously considered satisfactory with leakages of 10,000 ppm, such levels have now been found to be unacceptable for many applications. Desired emission levels for many industrial applications are below 500 ppm, and levels of less than 10 ppm for particularly toxic and carcinogenic materials would be desirable, particularly for those materials for which emission or handling standards have been established by various governmental agencies.
Current requirements for valve sealing have created a need for packing systems that exceed earlier performance requirements in a cost-effective manner.